Fuses

ABSTRACT

A fuse in which two current conductors are connected by fusible pellet, the connection between the current conductors being broken by mechanical spring action at the exceeding of a current threshold for which the pellet melts. One or each current conductor is combined and attached to an associated biased resilient element, thus forming an interruption element with both excellent mechanical and electrical characteristics for providing the wanted interruption action.

O United States Patent 1 51 3,639,874

Deelman 51 Feb. 1, 1972 [54] FUSES 2,239,390 4/1941 Jung et al "337/182X [72] Inventor: Gerard Jacobus Deelman Eindhoven 1,438,609 12/1922Perkms ..337/239 Netherlands FOREIGN PATENTS OR APPLICATIONS 1 1Assignee: Olvis Smeltzekeringenfabriek 1,146,253 11 1957 France ..337239 Utrecht, Netherlands Primary Examiner-Hemard A. Gilheany [22] 1969Assistant Examiner-Dewitt M. Morgan [21] Appl.No.: 879,442Attorney-Cushman, Darby& Cushman 57 ABSTRACT [52] U.S.Cl ..337/185,337/239 l [51] Int, Cl ]-[01h 35/03, H011 35/3 A fuse in which twocurrent conductors are connected by fusi- [58] Field ofSearch..337/159,165,166,182,183, ble Pellet, the connection between theCurrent conductors 337/135, 238, 239, 290, 297, 407 being broken bymechanical spring action at the exceeding of a current threshold forwhich the pellet melts. One or each [56] References Cited currentconductor is combined and attached to an associated biased resilientelement, thus forming an interruption element UNITED STATES PATENTS withboth excellent mechanical and electrical characteristics for providingthe wanted interruption action. 3,246,105 4/1966 Urant ..337/1832,400,491 5/ 1946 Duerkob ..337/185 X 2 Claims, 7 Drawing Figures 12 I31 l 6 14 12 I3 Y i x \e\ I. w

FUSES This invention relates to a fuse comprising two current conductorsconnected by a fusible pellet, the connection being broken when a giventhreshold value of current flowing through the conductors is exceeded asa result of mechanical spring action when the pellet melts.

Such fuses are known in the art. In Bulletin des SchweizerischenElectrotechnischen Vereins, 1962, page 589 ff., there are describedconstructions of slow-blow fuses in which, in a glass tube, two smallcurrent-carrying tension springs are interconnected by a fusible pellet.When the pellet melts, at a given temperature, the current is cut off bythe biased springs withdrawing to their equilibrium position.

Such fuses have some disadvantages, however. Since the pellet heating iscaused by the generation of heat from the current in the springs, thereis the danger that sudden overheating may result in a loss ofresiliency, which may have disastrous effects on the apparatus protectedby the fuse. This disadvantage is felt more strongly according as suchfuses are designed for lower fusing currents. While winding of smalltension springs is difficult enough in itself, the wires for suchlowcurrent fuses must also have a high specific resistance, the choiceof materials is still further restricted by the requirement that thewires must be solderable with low-melting alloys. Materials whichsatisfy both requirements have the disadvantage, however, that they losetheir resiliency at relatively low working temperatures.

The prior art has further proposed slow-blow fuses in which thecurrent-carrying tension spring is electrically bridged with a flexiblecopper wire. Also, such springs are sometimes coated with tin or copper.These solutions of the problem of loss of resiliency referred to,however, are often not effective, cumbersome in the manufacture, andcause undue variety in the characteristics of such fuses. Anotherdisadvantage of these fuses is that, particularly in constructions forlow-fusing currents, heat losses occur in the current conductors,resulting in highly inefficient fuses with relatively large powerdissipations. There is also a factor of uncertainty as far as the fusingrange is concerned.

it is an object of the present invention to eliminate the disadvantagesdescribed above.

The invention accordingly provides a fuse comprising a casing with inputand output means, and two current conductors with the one ends of saidcurrent conductors being connected by a fusible pellet and the otherends of said current conductors being connected to said input and outputmeans respectively, at least one of said current conductors beingdisposed closely along and attached to a biased resilient elementassociated with it and following the geometrical configuration of saidassociated resilient element, the one end of the said resilient elementbeing attached to the casing and the other end being in contact with thefusible pellet, so as to constitute an interruption element having bothmechanical and electrical characteristics for breaking by mechanicalspring action the electrical connection between said current conductorswhen a given threshold value of electrical current through said currentconductors for melting said pellet is exceeded.

Accordingly, in the fuse according to the present invention, thefunctions of resilient elements and current-carrying elements aresubstantially separated and as a consequence, the choice of material forresiliency characteristics is no longer coupled to the choice ofmaterialfor electrical characteristics. Such a separation is not new per se. lnDutch Patent Specification No. 24,318, there is described a fuse inwhich a fusible wire, which consists of two parts interconnected byafusible pellet, is biased by a noncurrent-carrying compression spring.Since, however, in that case, the current conductors are spaced from theresilient element, there is still the disadvantage of insufficientlyquick supply of heat from the condtlctors to the fusible pellet as aresult of heat losses in the current conductors. On the other hand, inthe fuse according to the present invention, we deliberately make use ofthe heataccumulating properties of the resilient material by disposingthe windings adjacent or closely around the resilient elements. Byvirtue of this arrangement. the resilient elements can serve asaccumulators for the heat dissipated by the windings, so that moreeffective and quicker heating can take place at the pellet.

In the fuse according to the invention, the resilient elements may besecured in insulating material formed integrally with the casing of thefuse; the free ends of these resilient elements may be held together bya fusible pellet.

Preferably the resilient elements have a core of resilient material,which is a poor heat conductor and has a low specific heat, for example,stainless steel.

It is also possible to make use of a resilient element consistingofinsulating material.

For low-current applications use can be made of a resilient elementaround which the current conductor has been disposed as a close thincurrent winding ofa conducting metal. Forthe case the resilient elementis formed of a metal core, such as stainless steel, said core may besurrounded by an insulating layer of for example enamel or syntheticresin material or the current winding may be coated with insulatingmaterial. The current windings may be produced by previously winding theresilient elements with a thin conductor, for example, an enameled wire,which may, for example, be made of a coppernickel alloy of high specificresistance. The current windings may further be united with theresilient elements solidly by heat treatment, if necessary addinglacquer or adhesive. By further securing the free ends of the currentwindings to terminals of the casing of the fuse in such a manner thatthese terminals are electrically insulated from the supporting points ofthe resilient members, it is achieved in a simple manner that theresilient members do not take part in the current conduction of thefuse.

One advantage of the fuse according to the present invention is thatthere is a greater choice of materials and design, and methods ofmanufacture may be varied. Thus as stated be fore the resilient coreneed not be of conductive material in the form of a wire or strip, butmay be made of insulating material, for example, of a glass fiber orstrand of glass fibers. Furthermore, it is not necessary for theresilient core to be soldered to the alloy of the pellet. The lattermay, for example connect two suitable points of the windings.

According to the invention windings may be built up from two or morethin conductors side by side, with the advantage ofa greater flexibilityand relatively low resistance. Instead of using a separate windingaround a resilient core, wemay also use an etch-printed conductor on aninsulation of synthetic resin material surrounding the resilient core.In this manner the fuse according to the invention may, for example, beadapted for use in printed circuits.

For high-current applications, where shorter and thicker currentconductors are needed, the current conductor instead of being woundaround its associated resilient element can be disposed adjacent andparallel to the resilient element to constitute a useful currentinterruption element. For attachment of the conductor to the resilientelement use can be made of a close thin winding around the so formedbundle. As is the case in the low-current application mentioned abovethere can be provided insulation between the resilient element and thecur rent conductor. However in many cases such an insulation can beomitted. Thus it is possible for example to constitute a fuse withcurrent interruption elements comprising a resilient element ofstainless steel combined to a bundle with a good conducting metal wire,said bundle surrounded by coil of a thin metal wire, closely woundaround said bundle.

So formed interruption elements have excellent characteristics forbreaking the current connection above a predetermined threshold value ofallowable electrical current.

The invention will be further described by way of example with referenceto the accompanying drawings.

FIG. 1 shows a fuse according to the invention including two resilientelements on which current conductors are wound;

FIG. 2 shown a fuse with an indicator contact;

FIG. 3 shows a fuse according to the invention designed particularly foruse with printed circuits;

FIG. 4 illustrates a fuse according to the invention in a form suitablefor being built into a cylindrical tube of electrically insulatingmaterial; and

FIG. 5 illustrates a fuse according to the invention in which theresilient element takes the form ofa helical tension spring, and

FIGS. 6 and 7 show high current fuses according to the invention inwhich are interruption elements consisting of a combined bundle ofresilient and electrically good conducting metal wires surrounded bythin metal windings.

Referring to FIG. I, there is shown a casing l, in which are securedterminals 2 and resilient elements 3. The resilient elements areprovided with current windings 5, the ends 4 of which are connected withthe terminals 2. The fusible pellet 6, which provides a conductiveconnection between the windings 5, holds the resilient elementstogether. Depending on the magnitude of the current and the ambienttemperature, blowing of the fuse will occur at the pellet 6. Sudden,very large currents however, will cause the current to be broken owingto the melting of the ends 4, which in such embodiments provides anadditional protection.

In FIG. 2, there is shown a fuse according to the invention providedwith an indicator contact, the conductive, resilient element 3 beingkept under tension by a thin conductor 7, which connects the terminal 2with the fusible pellet 6 at the end of the current winding. The winding5 is insulated from the resilient element 3. When the pellet 6 melts,the spring 3 effects a conductive connection between the auxiliarycontacts 8, which energizes an alarm system.

FIG. 3 shows a fuse according to the invention designed particularly foruse with printed circuits. The resilient element 3, provided with acurrent winding 5, is clamped in a panel 9 provided with a printedcircuit 10. The fusible pellet 6 connects the winding 5, which is sodimensioned that it has a resistance value suitable for the circuit,with the printed circuit 10 and also keeps the resilient element 3 undertension.

The fuse shown in FIG. 4 has a form particularly suitable for beingbuilt into a cylindrical tube of electrically insulating material. Acasing 1 of, for example, heat-resistant synthetic resin material housesterminals and the resilient elements 3. The fusible pellet 6 connectsthe windings 5 and keeps the resilient elements 3 under tension. Thecasing is surrounded by a cylindrical tube 11, including metal caps 12soldered to the terminals.

FIG. 5 shows a fuse according to the invention incorporating a resilientelement 3 in the form ofa helical tension spring surrounded by a winding5. The tension spring is anchored in a casing 1 and is kept undertension by a conductor 7, which is conductively connected to the winding5 by the fusible pellet 6. The fuse is accommodated in a tube 11 ofelectrically insulating material, provided with conductive caps 12.

FIGS. 6 and 7 relate especially to high-current fuses. In FIG. 6 thereis shown a fuse comprising a glass tube 11, sealed by two conductingmetal end caps 12, cemented to the glass tube by a cementing l3.

Enclosed in the glass tube there are two interruption elements eachcomprising two wires of stainless steel 3 and one wire of silver 5combined to a bundle. Said bundle is surrounded by a thin silver winding14 for attachment purposes.

The so formed interruption elements are clamped for biasing in the glasstube and contacted to the metal caps with their one ends, the other endsbeing contacted to each other by a fusible tin solder pellet 6. In thisembodiment and insulation between steel wire and silver wire can beomitted as the main current will flow through the good conducting silverwire.

The fuse shown in FIG. 7 is of the same configuration as the foregoingexcept that the interruption elements are clenched between the caps andthe glass tube for biasing the springs.

Of course the fuses shown are only exemplary embodiments shown forillustration purposes.

There are numerous variations possible which may fall under the scopeofthc invention. So it is for example possible to provide theinterruption elements with a number of conducting wires 5 and a numberof resilient wires 3. It is also possible to use for high-currentpurposes a fuse of the type shown in FIG. 5 with one helical-typeinterruption element constituted in accordance with the bundle principlementioned above and comprising the first current conductor whereas thesecond current conductor is single silver wire.

Such a configuration gives a special protection for sudden veryhigh-current pulses, for the current conductor 7 acts as acurrent-limiting element that will melt at very high and sustainedovercurrents.

Embodiments with two opposite helical-spring-type interruption elementsare also possible both in the design wherein the current conductor iswound around the resilient element as in the design wherein the currentconductor is disposed along and parallel to the resilient element.

The fuses according to the invention show numerous advantageous aspects.By effecting, on the one hand, a separation between resilient elementsand conductive elements, and on the other hand yet ensuring amechanically coherent unit, the invention provides a reproducible fusewhich permits an optimum choice of materials, both for resiliencycharacteristics and for electrical characteristics. Also it providesreliable current protection, and a compact and sturdy construction. Thusit is possible to construct sandfilled fuses with low heat dissipation.Furthermore the methods of manufacture are simple and suitable forproduction on a continuous basis. In addition, for the selection of thefusible pellet, one is not limited to a conductive soldered connection,but may, especially for low-current application, use nonconductivesubstances, for example, synthetic resins, having a desired meltingpoint, and keeping thus the contact between the conductors closed.

In cases wherein a tin solder pellet is used, too much flowing of thetin solder along the contacted ends of the two current conductors isprevented because of the fact that the current conductors combined withthe resilient elements are either formed as a coil either surrounded bya coil, thus limiting the tin flow in axial direction.

Iclaim:

1. A fuse comprising a casing with input and output means, and twocurrent conductors with the one ends of said current conductors beingconnected by a fusible pellet and the other ends of said currentconductors being connected to said input and output means respectivelyat least one of said current conductors being disposed adjacent andparallel to a biased resilient element associated with it and followingthe geometrical configuration of said associated resilient element, saidone conductor being attached to the resilient element by a winding ofthin metal wire closely wound around the assembly of the conductor andthe resilient element, the one end of the said resilient element beingattached to the casing and the other end being in contact with thefusible pellet, so as to constitute an interruption element having bothmechanical and electrical characteristics for breakingby mechanicalspring action the electrical connection between said current conductorswhen a given threshold value of electrical current through said currentconductors for melting said pellet is exceeded.

2. A fuse comprising a casing with input and output means, and twocurrent conductors with the one ends of said current conductors beingconnected by a fusible pellet and the other ends of said currentconductors being connected to said input and output means respectivelyat least one of said current conductors being disposed closely along andattached to a biased resilient element associated with it and followingthe geometrical configuration of said associated resilient element, saidresilient element comprising a bundle of at least two'wires of a poorelectrical conducting resilient metal, said bundle and said oneconductor being surrounded by a coil of thin metal wire closely woundaround said bundle and said one conductor, one end of the said resilientelement being attached to the casing and the other end being in contactwith the fusible pellot, so as to constitute an interruption elementhaving both mechanical and electrical characteristics for breaking bymechanical spring action the electrical connection between said currentconductors when a given threshold value of electrical current throughsaid current conductors for melting said pellet is exceeded. 5

1. A fuse comprising a casing with input and output means, and twocurrent conductors with the one ends of said current conductors beingconnected by a fusible pellet and the other ends of said currentconductors being connected to said input and output means respectivelyat least one of said current conductors being disposed adjacent andparallel to a biased resilient element associated with it and followingthe geometrical configuration of said associated resilient element, saidone conductor being attached to the resilient element by a winding ofthin metal wire closely wound around the assembly of the conductor andthe resilient element, the one end of the said resilient element beingattached to the casing and the other end being in contact with thefusible pellet, so as to constitute an interruption element having bothmechanical and electrical characteristics for breaking by mechanicalspring action the electrical connection between said current conductorswhen a given threshold value of electrical current through said currentconductors for melting said pellet is exceeded.
 2. A fuse comprising acasing with input and output means, and two current conductors with theone ends of said current conductors being connected by a fusible pelletand the other ends of said current conductors being connected to saidinput and output means respectively at least one of said currentconductors being disposed closely along and attached to a biasedresilient element associated with it and following the geometricalconfiguration of said associated resilient element, said resilientelement comprising a bundle of at least two wires of a poor electricalconducting resilient metal, said bundle and said one conductor beingsurrounded by a coil of thin metal wire closely wound around said bundleand said one conductor, one end of the said resilient element beingattached to the casing and the other end being in contact with thefusible pellet, so as to constitute an interruption element having bothmechanical and electrical characteristics for breaking by mechanicalspring action the electrical connection between said current conductorswhen a given threshold value of electrical current through said currentconductors for melting said pellet is exceeded.